Molded plastic stress-distributing bushing



Sept. 19, 1950 l. w. A. KIRKWOOD El AL 2,523,219

MOLDED PLASTIC STRESS-DISTRIBUTING BUSHING Filed Feb. '7, 1945 a a, i Inventor Patented Sept. I9, 1950 MOLDED PLASTIC STRESS-DISTRIBUTING BUSHING Y Ian Ward. Anderson Kirkwood, Newcastle-n- Tyne, James Sibbald Gillhespy, Riding Mill, and Forster Jeflrey, Wallsend, England, assignors to A. Reyrolle & Company Limited, Hebburn-on-Tyne, England, a company of Great Britain Application February 7, 1945, Serial No. 576,584 In Great Britain February 15, 1944 2 Claims. 1

This invention relates to electric insulators and is concerned with the provision of stress grading layers or stress shields to distribute the electrical stress or prevent Corona discharge from an electrode.

In the case of an orifice insulator which is wound from synthetic-resin-impregnated paper 7 the incorporation of one or more conducting layers during the winding is a relatively easy matter, but considerable difficulty arises when conditions of high humidity for example make it preferable to use a moulded or ceramic bushing.

. It has been proposed to apply a metal sprayed band of suitable width within an orifice insulator in the region of the electrode but it then becomes necessary to provide against discharge from the edge of this band. If a layer of insulation is applied to the band the difiiculty arises of securing a satisfactory junction with the material of the main insulator since if the joint is not perfect harmful discharges may still take place.

According to the present invention an insulator is provided with a stress grading layer or stress shield in the form of a separate unit comprising the layer embedded in an insulating sheath which insulates its ends aswell as its inner and outer surfaces the said unit being secured to the main insulator.

The invention is particularly applicable to moulded insulators in which case the unit may comprise a laminated tube wound of synthetic resin-impregnated paper in which a metallic layer is embedded during the winding. The paper 7 serves to locate the metallic layer in the insulator and further stiffens a conducting cylinder which is subject to axial pressure during the moulding of the main insulator.

The invention is applicable to insulators of any sort for which it is considered a convenient Way of providing a stress shield or grading layer. It is particularly applicable to insulators of vitreous or ceramic materials such as porcelain or of plasties.

In the case of insulators formed of plastic materials an important feature of the invention is that the applied unit and the main insulator can be cured simultaneously.

The stress shield unit may be secured to the main insulator by shrinking or alternatively the unit may be machined, externally or internally as the case may be, to a driving fit, and forced into or on to the main insulator with or without treatment with an insulating adhesive.

Alternatively in the case of a moulded main insulator the unit may be incorporated during the moulding operation by inserting the semi-cured unit in the mould with the moulding powder or other material from which the main insulator is moulded, for example by heat and pressure. In this case the unit may be incorporated in positions which it could not reach by being forced into or on to a preformed main insulator, for example it may be recessed into the middle of a cylindrical external or internal surface, or may even be wholly or partly embedded in the material of the main insulator.

Certain specific embodiments of the invention will now be described With reference to the accompanying drawings in which:

Figures 1 to 3 are diagrammatic cross-sections of insulators constructed in accordance with the invention and Figure 4 is a diagram indicating the method of moulding an insulator in accordance with the invention.

Figure 1 shows an orifice insulator comprising a main insulator Aof vitreous or ceramic material such as porcelain. In order to incorporate a stress shield or stress-grading layer in the insulator an auxiliary unit is formed consisting of a tube B wound from synthetic-resin-impregnated paper having the shield or layer C of thin metal foil embedded in its during the winding operation. This unit is machined on its outer surface to be a driving fit in the main insulator and is forced into the latter with or without treatment With an insulating adhesive. The conducting layer may be provided with a flexible connector D as shown or other convenient connecting means passing through the insulation for connection to the electrode, in which case the layer serves as a stress shield. Alternatively or in addition there may be one or more isolated layers to serve as stress-grading layers.

Figure 2 shows an arrangement in which the synthetic-resin-impregnated paper sleeve B is secured to the outer surface of a porcelain bushing insulator A. In this case the flexible lead D is taken out to the metal fiange (not shown) on which the insulator is mounted.

Figure 3 shows the application of the invention to a moulded plastic insulator, the layer in the synthetic-resin-impregnated paper sleeve being connected at E to a surrounding metal flange F forced on to it. It will be seen that in this construction the main insulator covers both ends of the auxiliary unit, an arrangement that would not be possible with a preformed main insulator but is rendered possible by moulding the main insulator round the auxiliary unit, for example as indicated diagrammatically in Figure '4.

Figure 4 shows the semi-cured synthetic-resinimpregnated paper sleeve B incorporating the conducting layer C which is surrounded by the moulding powder or other form of moulding plastic material G in the mould H. The auxiliary unit is shown as situated at one end of the main insulator but it will be appreciated that it can equally well be disposed between the ends and may be either in its outer surface or its inner surface or even may be completely embedded in the moulded main insulator. In the case of an insulator formed of a plastic both the main insulater and the auxiliary unit may be cured simultaneously.

What we claim as our invention and desire to secure by Letters Patent is:

l. A composite electric insulator comprising a main insulating part and a subsidiary part, said parts being firmly united together to form a single insulating body whereof the subsidiary part consistituting a stress-grading layer cornprises a laminated insulating sheath of wound paper impregnated and bonded together with synthetic-resin and at least one conducting layer embedded between the laminations, said laminations insulating both ends and the inner and outer surfaces of the conducting layer, while the main insulating part is a single piece of homogeneous molded synthetic-resin extending in contact with both end faces and a cylindrical surface of the said sheath.

2. A composite electric insulator which comprises a preformed subsidiary part consisting of a laminated and impregnated insulating sheath with at least one conducting layer embedded between the laminations, said laminations insulating both ends and the inner and outer surfaces of the conducting layer, and a main insulating part integral with said subsidiary part and consisting of a homogeneous body of synthetic resin formed by a moulding process and integrated with saidpre'formedsub'sidiary part by said moulding process.

IAN WARD ANDERSON KIRKWOOD. JAMES SIBBALD GILLHESPY. FORSTER JEFFREY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,657,249 Eby Jan. 24, 1928 1,693,327 Abrahams Nov. 27, 1928 1,759,419 Rump May 20, 1930 2,086,078 Haefely July 6, 1937 2,091,107 Reichmann Aug. 24, 1937 2,287,201 Scott et a1 June 23, 1942 2,322,215 Kirkwood June 22, 1943 FOREIGN PATENTS Number Country Date 67,318 Switzerland Jan. 26, 1914 342,416 Germany Oct. 18, 1921 368,030 Germany Jan. 30, 1923 373,056 Germany Apr. 7, 1923 

1. A COMPOSITE ELECTRIC INSULATOR COMPRISING A MAIN INSULATING PART AND A SUBSIDIARY PART, SAID PARTS BEING FIRMLY UNITED TOGETHER TO FORM A SINGLE INSULATING BODY WHEREOF THE SUBSIDIARY PART CONSISTITUTING A STRESS-GRADING LAYER COMPRISES A LAMINATED INSULATING SHEATH OF WOUND PAPER IMPREGNATED AND BONDED TOGETHER WITH SYNTHETIC-RESIN AND AT LEAST ONE CONDUCTING LAYER EMBEDDED BETWEEN THE LAMINATIONS, SAID LAMINATIONS INSULATING BOTH ENDS AND THE INNER AND OUTER SURFACES OF THE CONDUCTING LAYER, WHILE THE MAIN INSULATING PART IS A SINGLE PIECE OF HOMOGENEOUS MOLDED SYNTHETIC-RESIN EXTENDING IN CONTACT WITH BOTH END FACES AND A CYLINDRICAL SURFACE OF THE SAID SHEATH. 